Unknown number called. No message left. Suspect number.

Yes I got four attempted calls from them yesterday. Did not answer - I assumed they were some form of spammer.

Called my mobile immediately after I had screened a call on my home phone answering machine.

Not sure who it is; but I have observed this this pattern recently from Apple Marketing.
Although the number has been different in the past.

Scam caller. Blocked it. Didn't answer and they never left a message. Don't trust any number beginning with (03)

Caller: Apple Marketing Group

They called our landline first, but hung up when I picked up; they then called my mobile, but as the screen said 'potential fraud', I didn't answer.
Stop Press: I just called them and there was a recorded message saying, Thank you for calling Apple Marketing Group/Fundraising Group.

Rang me too but didn’t leave a message.

I did not answer as the phone number is unknown. Left blank voice message.